ec8da8f12c
Co-authored-by: Mikhail Bashkirov <mikhail.bashkirov@ing.com> Co-authored-by: Thijs Louisse <thijs.louisse@ing.com> Co-authored-by: Joren Broekema <joren.broekema@ing.com> Co-authored-by: Gerjan van Geest <gerjan.van.geest@ing.com> Co-authored-by: Erik Kroes <erik.kroes@ing.com> Co-authored-by: Lars den Bakker <lars.den.bakker@ing.com>
62 lines
2.5 KiB
Markdown
62 lines
2.5 KiB
Markdown
# ModelValue
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The modelValue or model can be considered as the ‘aorta’ of our form system.
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It is the single source of truth; not only for the current state
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of the form, also for all derived states: interaction, validation, visibility and other states are
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computed from a modelValue change.
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## Single source of truth
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ModelValues are designed to provide the Application Developer a single way of programmatical
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interaction with the form for an Application Developer.
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### One single concept for Application Developers
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Application Developers need to only care about interacting with the modelValue on a form control
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level, via:
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- `.modelValue`
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- `@model-value-changed`
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> Internal/private concepts like viewValue, formattedValue, serializedValue are therefore not
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recommended as a means of interaction.
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### One single concept for internals
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Internally, all derived states are computed from model-value-changed events.
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Since the modelValue is computed 'realtime' and reflects all user interaction, visibility and
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validation states, we can guarantee a system that enables the best User Experience
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(see Interaction States).
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## Unparseable modelValues
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A modelValue can demand a certain type (Date, Number, Iban etc.). A correct type will always be
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translatable into a String representation (the value presented to the end user) via the `formatter`.
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When the type is not valid (usually as a consequence of a user typing in an invalid or incomplete
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viewValue), the current truth is captured in the `Unparseable` type.
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For example: a viewValue can't be parsed (for instance 'foo' when the type should be Number).
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The model(value) concept as implemented in lion-web is conceptually comparable to those found in
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popular frameworks like Angular and Vue.
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The Unparseable type is an addition on top of this that mainly is added for the following two
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purposes:
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- restoring user sessions
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- realtime updated with all value changes
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### Restoring user sessions
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As a modelValue is always a single source of truth
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### Realtime updated with all value changes
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As an Application Developer, you will be notified when a user tries to write the correct type of
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a value. This might be handy for giving feedback to the user.
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In order to check whether the input is correct, an Application Developer can do the following:
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```html
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<lion-input @model-value-changed="${handleChange}"></lion-input>
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```
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```js
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function handleChange({ target: { modelValue, errorState } }) {
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if (!(modelValue instanceof Unparseable) && !errorState) {
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// do my thing
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}
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}
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```
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